In a typical alarm system within a building, such as a fire or burglar alarm system, many types of sensors, detectors, lights, strobes, sounders and other associated devices may be located throughout the building as part of the system. Groups of these devices are often wired together along one or more pairs of electrical lines used to supply power and communications to the devices. A group of such devices wired on a commonly shared pair of lines is often referred to as a line of devices. Many separate lines of devices typically connect back to a control panel that controls the overall operation of the alarm system. A line of devices is usually associated with a certain zone of the building and/or a certain type of device. For example, one floor of a multi-story building may have all of its smoke detectors wired together on a line that connects back to the control panel.
In the alarm system, it is important to monitor the integrity of the line of devices to ensure that, in the case of an emergency, the devices will function properly. Such monitoring has been performed in the prior art using a supervisory current, as illustrated in FIG. 1.
An alarm system is provided generally as 10. The system 10 has a plurality of alarm devices 12-1, 12-2, 12-3, 12-4 electrically and alternately connected to a first voltage source 14 and a second voltage source 26, and to respective zero volt connectors 44 and 28, by electrical conductor 16. The alarm devices 12-1 through 12-4 are wired together in a parallel configuration. The system 10 also includes a first switch 18 and a second switch 20. Each switch 18, 20 can determine which source 14, 26 will power the alarm system 10.
The wiring integrity of the system 10 can be monitored in a supervisory state. When the system 10 monitors the integrity of the alarm devices 12 and electrical conductors 16 in a supervisory state, the first switch 18 engages an up position 22 while the second switch 20 engages a down position 42. Such contacting of the switches 18, 20 allows a supervisory current to travel from the first source 14 to a first zero volt connection 28. From the first voltage source 14, the supervisory current travels through an end-of-line resistor 30 and through a resistor 32 prior to reaching the first zero volt connection 28. In the supervisory state, alarm devices 12-1, 12-2, 12-3, 12-4 are inactive and draw a minimal amount of current from the first voltage source 14.
The voltage across the resistor 32, which indicates the level of current through conductor 16, is monitored by a wire integrity sensor 34. If the voltage within the resistor 32 remains relatively constant, as compared to a reference voltage 36, a status signal can be sent to a controller 38 indicating a proper line integrity of the system 10. The controller 38 can then indicate to a user that the wiring of the system 10 contains no breaks. In the case where the voltage remains constant, the wire integrity sensor 34 can continue to monitor the voltage across the resistor 32. A voltage drop across the resistor 32, as compared to the reference voltage 36, can indicate a problem in the electrical conductors 16 which prevents current from flowing to the alarm devices. If the wire integrity sensor 34 detects a drop in the voltage within the resistor 32, the wire integrity sensor 34 sends a status signal to the controller 38, indicating that there is a break in the line integrity of the system 10. The controller 38 can then indicate to a user the existence of a break in the wiring integrity of the system 10.
During an alarm state, the first switch 18 engages in the down position 24 while the second switch 20 engages the up position 40. Contacting of the switches 18, 20 in this manner allows an alarm-mode current to travel from a second voltage source 26 to a second zero volt connection 44. The second voltage source provides 24 volts to the system 10. In an alarm state, the alarm devices 12-1, 12-2, 12-3, 12-4 are active and draw significant current from the second voltage source 26. Current from the second voltage source 26 travels through each alarm device 12-1, 12-2, 12-3, 12-4 and toward the second zero volt connection 44. To monitor the system 10 during an alarm state, the system 10 includes a monitor 46 and a fuse 50.
During an alarm state, the monitor 46 compares a measured voltage of the system 10 with a reference voltage 48 of approximately zero volts. In the case where the fuse 50 remains intact, the monitor 46 measures zero volts. The monitor 46, in detecting no difference between the measured voltage and the reference voltage 48, can then send a status signal to the controller 38 indicating that the fuse is intact.
In the case where one of the alarm devices 12-1 through 12-4 develops a short circuit during an alarm state, the alarm device will draw an increased amount of current, thereby leading to an over current situation in the system 10. The over current in the system 10, in turn, causes the fuse 50 to trip or blow. With the fuse tripped, the monitor 46 will measure 24 volts from the system 10 and compare this measured voltage to the reference voltage 48. In the case of a tripped fuse, the monitor 46, in detecting a difference between the measured voltage and the reference voltage 48, sends a status signal to the controller 38 to indicate a short circuit in one of the alarm devices 12-1 through 12-4. The controller 38, in turn, can indicate to a user the existence of a short circuit in one of the alarm devices. Monitoring of an alarm system 10 in this manner, during an alarm state, has been performed using the Simplex 4010 system (Simplex Time Recorder, Gardner, Mass.).
While the aforementioned monitors can determine line integrity during a supervisory state and a short circuit in an alarm device in an alarm state, the monitors do not indicate where in the system a break has occurred during a supervisory mode or whether a break has occurred in the alarm mode. The monitors also fail to indicate which alarms are inoperative due to a break in the wiring of the system or due to a failure of an alarm device. Information regarding the location of the break and the operability of the alarms can be useful to emergency personnel. Without alarm notification, occupants may remain in a building during an alarm state, for example. Knowledge of where a break in line integrity occurs can provide emergency personnel with information regarding which occupants should be personally warned of an alarm state in a building.
During a fire emergency in the aforementioned alarm systems, the electrical conductors and alarm devices themselves are subject to damage caused by a fire or the resulting heat. Certain types of Circuit Integrity wiring can withstand direct flame for up to two hours. The characteristics of the wire, however, will change with this exposure. For example, the resistance of the wire will increase when exposed to direct flame. With such a change in the wire, the alarms used to warn of the fire may become inoperative. The change in resistance of the wiring, leading to alarm failure, cannot be detected with the current alarm systems.
The present alarm system detects the failure of an alarm device connected to the system. The alarm system will also detect not only a break in the line integrity of the system, but the location of the break. Furthermore, the alarm system can detect the change in resistance of the wiring in the system caused by exposure to heat which, in turn, can predict the potential failure of an alarm system.
The alarm system can include an electrical conductor, a plurality of alarm devices powered from the electrical conductor and a load sensor which senses the electrical load on the electrical conductor to indicate failure of one or more devices. The electrical load measured by the load sensor is proportional to the number of alarm devices powered from the electrical conductor. A decrease in the electrical load of the system indicates failure of at least one alarm device. The alarm system can also include at least one wire integrity sensor to monitor for breaks in the electrical conductor during supervisory mode.
The plurality of alarm devices in the system can be notification appliances, such as audible devices or light strobes. The alarm devices can also be sensors, such as smoke or temperature sensors. The load sensor can measure either current in the electrical conductor, such as by sensing voltage across a resistor connected in series with the electrical conductor, during an alarm state and compare this measurement against a baseline or initial electrical load value. Any deviation between the initial load and measured load indicates failure of an alarm device. The initial electrical load in the alarm system can be measured during the initialization of the system. When the load sensor is active, during an alarm state, the sensor indicates the number of alarm devices active in the alarm system.